Saw blades for cutting wood, metal, and the like often have a plurality of teeth cut into the blade's outer edge. In many cases, the teeth are tipped with a hard material such as carbide or STELLITE, a cobalt alloy, to reduce wear and maintain sharpness. An apparatus for tipping the teeth of a saw blade is disclosed in my copending application, filed concurrently herewith and entitled Method and Apparatus for Tipping Teeth of Saw Blades, Ser. No. 07/067,645, incorporated herein by reference.
When a tooth is tipped, it is oversized and must be ground to desired dimensions and tangential and radial clearance angles for cutting the proper kerf. The tangential clearance angle is viewed from above the tooth and measures the inward taper of the tooth from the tooth face rearward. The radial clearance angle is viewed from the face of the tooth and measures the inward taper from the tooth top toward the blade.
Prior apparatus for grinding tipped saw teeth to proper dimension and clearance angles, such as manufactured by Vollmer Werke Maschinenfabrik GmbH of Germany, include a pair of opposed grinding wheels adjusted to grind teeth to the desired compound taper formed by the tangential and radial clearance angles. The two grinding wheels are set a predetermined distance apart to grind the opposite sides of a tooth secured in a grinding position. The following tooth on the blade is then advanced to the grinding position and the operation repeated. This continues until all teeth of the blade are ground to the preselected dimension. The teeth are then measured manually for the desired dimension; and if additional material must be removed, the grinding wheels are reset and each tooth in succession is again ground.
U.S. Pat. No. 4,418,589 to Cowart, Sr., teaches the use of a programmable controller for supervising the grinding of saw blade teeth. However, Cowart, Sr., does not contemplate automated measurement of the resultant tooth dimensions. Instead, the controller is used to supervise the advancement and retraction of the grinding wheels in response to signals indicating the position of and the pressure on a pawl of an indexing system. The travel of the grinding wheels is controlled by precision limit switches.
In U.S. Pat. No. 3,842,545 to Possati, the dimensions of the article being machined are sensed by an electronic sensor and are fed to an electronic controller. The controller computes from this dimension data the rate at which material is being removed from the article. When the sensors determine that the article has been machined within a preset value of its desired dimension, the measuring sensors are physically withdrawn. The machine tool then continues operation for a length of time sufficient, based on the computer rate at which material is being removed, for the article to be machined to its desired dimension. The withdrawal of the measuring sensors before the machining is complete allows the apparatus to more rapidly disengage the finished article and accept the next article for machining.
Other prior apparatus rely exclusively on mechanical stops to limit the travel of sawtooth grinding wheels. Examples of such systems are U.S. Pat. Nos. 3,611,839 to Idel and 4,366,728 to Beck et al. The Idel patent discloses an apparatus for sharpening and resetting teeth on a band saw. The band is spring biased towards the grinding wheel until a stop member prevents its further travel. The principal feature of the Idel patent is an arrangement that allows the sharpening angles to be reset readily to adapt to saws having differently shaped teeth.
The Beck et al. '728 patent discloses a machine for preparing hard alloy tipped saw blades. A saw blade is clamped into the machine and brazing and grinding tools are sequentially operated to remove a damaged saw tip, recondition the plate seat, braze on a new tip, and grind the new tip to the desired shape. The grinding operation is effected by advancing a pair of grinding wheels towards the blade a predetermined distance and then retracting the wheels. No feedback control is provided.
These and other prior grinding apparatus suffer from a number of drawbacks. For one, the apparatus are labor intensive, requiring manual measurement of the dimensions desired after each grinding. For another, they do not treat each tooth individually. No means for compensating for misaligned teeth or worn grinding mechanisms are provided. A third drawback is the wear on the apparatus. Each tooth must be ground a number of times as the blade is repeatedly passed between the grinding wheels. This repeated grinding causes causes the apparatus to wear out more quickly than if fewer grinds were required.